Electronic mail, often abbreviated to e-mail, email, or simply mail, is a store-and-forward method of writing, sending, receiving and saving messages over electronic communication systems. The term "email" (as a noun or verb) applies to the Internet email system based on the Simple Mail Transfer Protocol, to network systems based on other protocols and to various mainframe, minicomputer or intranet systems allowing users within one organization to send messages to each other in support of workgroup collaboration. Intranet systems may be based on proprietary protocols supported by a particular systems vendor, or on the same protocols used on public networks. Email is often used to deliver bulk unsolicited messages, or "spam", but filter programs exist which can automatically block, quarantine or delete some or most of these, depending on the situation.